PA34 View Datasheet(PDF) - Unspecified
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PA34 Datasheet PDF : 5 Pages
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OPERATING
CONSIDERATIONS
PA34
+VS ≤ 20V
DB1
DB2
7 3 10
CB1
5
CB2
SPEAKER
Using this voltage as a feedback source allows expressing
the gain of the circuit in amperes vs input voltage. The transfer
funcion is approximately:
IL= (VIN – VREF) *RIN/ RFB/ Rs
In the illustration, resistors RIN, RFB and RS determine
gain.
8
FIGURE 3. SIMPLE BOOTSTRAPPING IMPROVES POSITIVE
OUTPUT SWING. CONNECT PINS 3 AND 10 TO VS IF NOT
USED. TYPICAL CURRENTS ARE 12mA EACH.
VBOOST pin requires approximately 10–12mA of current.
Dynamically it represents 1K Ω impedance. The maximum
voltage that can be applied to VBOOST is 40 volts with
respect to –VS . There is no limit to the difference between
+VS and VBOOST.
Figure 3 shows a bootstrap which dynamically couples the
output waveform onto the VBOOST pin. This causes VBOOST
to swing positive from it's initial value, which is equal to +VS
-0.7 V (one diode drop), an amount equal to the output. In
other words, if VBOOST was initially 19.3, and the output
swings positive 18 Volts, the voltage on the VBOOST pin
will swing to 19.3 -0.7 + 18 or 36.6. The capacitor needs
to be sized based on a 1K Ω impedance and the lowest
frequency required by the circuit. For example, 20Hz will
require > 8uF.
ISENSE
The ISENSE pin is in series with the negative half of the
output stage only. Current will flow through this pin only when
negative current is being outputted. The current that flows
in this pin is the same current that flows in the output (if
–1A flows in the output, the ISENSE pin will have 1A of
current flow, if +1A flows in the output the ISENSE pin will
have 0 current flow).
The resistor choice is arbitrary and is selected to provide
whatever voltage drop the engineer desires, up to a maximum
of 1.0 volt. However, any voltage dropped across the resistor
will subract from the swing to rail. For instance, assume a
+/–12 volt power supply and a load that requires +/–1A. With
no current sense resistor the output could swing +/–10.2
volts. If a 1 Ω resistor is used for current sense (which
will drop 1 Volt at 1 Amp) then the output could swing
+10.2, –9.2 Volts.
Figure 4 shows the PA34 ISENSE feature being used to
obtain a Transconductance function. In this example, amplifier
"A" is the master and amplifier "B" is the slave. Feedback
from sensing resistors RS is applied to the summing network
and scaled to the inverting input of amplifier "A" where it is
compared to the input voltage. The current sensing feedback
imparts a Transconductance feature to the amplifiers transfer
function. In other words, the voltage developed across the
sensing resistors is directly proportional to the output current.
+VS
C
VBIAS
B
R
RL IL
VIN
A
R
RFB
RIN
RS
RS RIN RFB
–VS OR GND
VREF
FIGURE 4. ISENSE TRANSCONDUCTANCE BRIDGING
AMPLIFIER
VBIAS should be set midway between +Vs and -Vs, Vref
is usually ground in dual supply systems or used for level
translation in single supply systems.
MOUNTING PRECAUTIONS
1. Always use a heat sink. Even unloaded, the PA34 can
dissipate up to 3.6 watts. A thermal washer or thermal
grease should always be used.
2. Avoid bending the leads. Such action can lead to internal
damage.
3. Always fasten the tab to the heat sink before the leads are
soldered to fixed terminals.
4. Strain relief must be provided if there is any probability of
axial stress to the leads.
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PA34U REV. 1 JANUARY 2001© 2001 Apex Microtechnology Corp.
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